Problem URL: Vowels of all substrings

We can use bottom-up dynamic programming to solve the problem. We will use a variable vowels to store the number of vowels in the string. Then we will iterate over the string and update vowels accordingly. Finally, we will return vowels.

class Solution:
    def countVowels(self, word: str) -> int:
        vowel = {'a':0, 'e':0, 'i':0, 'o':0, 'u':0}
        n = len(word)

        for i in range(n):
            if word[i] in vowel:
                vowel[word[i]] += (i+1)*(n-i) 

        return sum(vowel.values())

Time complexity: O(n)
Space complexity: O(1)